The use of sarcosinate surfactants, and in particular, N-Acyl sarcosinates in the manufacture of soaps and for other personal care and industrial applications is well known. Typically, the sarcosinate is used in the form of its sodium, potassium or ammonium salt solution. N-Acyl sarcosinates are produced commercially by the Schotten-Baumann reaction of the sodium salt of sarcosine with the appropriate fatty acid chloride under carefully controlled conditions: ##STR1## where R is typically a fatty acid of chain length C.sub.10 to C.sub.18, commonly made from lauric, coconut, palmitic, myristic or oleic acid. After the reaction is complete, the crude sodium salt is acidified to liberate the free fatty sarcosine acid which is separated from the aqueous by-products. It then is neutralized to a salt form. Sarcosinates such as sodium lauroyl sarcosinate, sodium cocoyl sarcosinate and sodium myristoyl sarcosinate are commercially available under the trademark HAMPOSYL.RTM. from Hampshire Chemical Corp., as 30% active solutions in water. To produce soap bars, much of the water is removed, which may require heating the mixture to temperatures in the vicinity of 150.degree. C. The 30% solutions are costly to package and ship, and require preservatives, which are coming under close scrutiny. Some are toxic, potential carcinogens or sensitizers. Formaldehyde, which was previously used to preserve sarcosinates, is no longer acceptable. It is more favorable to ship an unpreserved raw material and allow the customer to preserve his finished product as he wishes, since different customers favor different preservative systems. Unlike aqueous solutions, the solid products are not susceptible to biodegration.
More concentrated sarcosinate solutions are difficult to produce because of high viscosity. Furthermore, as the pH of the N-Acyl sarcosine is raised from pH 2 towards pH 5, even enroute to 30% solutions gel phases of high viscosity are often encountered (particularly with myristoyl and oleoyl sarcosines), which make production of a uniform and homogeneous product difficult and time consuming. Above 30% concentrations, at any pH, the solutions become too viscous to handle. This is why solutions are offered at 30% concentrations. (Sodium oleoyl sarcosinate is not offered as a solution because it becomes too viscous to hande above 15% active.) As a result, when a product of nearly 100% activity is required, the 30% solution must be spray dried, which is a difficult and costly process.
It is therefore an object of the present invention to provide a process for producing concentrated sarcosinate solutions while avoiding the viscous, gel phases typically encountered in prior art processes. Benefits of concentrated product include reduced shipping cost and no requirements for preservatives.